Earlier this month the Duke marked his 96th birthday with a gun salute in Green Park.

He has enjoyed good health throughout much of his life, recovering from a blocked coronary artery in 2011 and a bladder infection in 2012, the latter leading him to miss the majority of the Queen’s Diamond Jubilee celebrations.

Earlier this year he announced he would step down from public royal duties in the autumn, but Buckingham Palace said it was not health-related.

The Duke is an advocate of healthy eating combined with exercise and is well-known for his robust constitution.

He takes the stairs rather than lifts and still fits into the uniform he wore on his wedding day.

Last year the 96-year-old told a flu expert at a research centre he had not had the illness for 40 years.

AP:Associated Press

The Duke joined the Queen on Saturday for her official birthday at the Trooping the Colour parade

When the Duke was in his 70s one of the Queen’s former physicians described him as “astonishingly fit for a man of his age”.

Just ahead of his 95th birthday last June, he pulled out of the Battle of Jutland anniversary events following medical advice, with his son-in-law, Vice-Admiral Sir Tim Laurence, saying he had a “minor ailment”.

Both the Queen and the Duke fell ill with heavy colds before Christmas, forcing them to delay their trip to Sandringham by a day.

But while the Queen was not well enough to attend the Christmas Day church service nor the New Year’s Day one, Philip went to both.

Last weekend he helped the Queen celebrate her official 91st birthday at the annual Trooping the Colour parade.

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